Rewatching Man of Steel, and can't for the life of me figure out why a race of people with a world ship need to populate a habited planet? Especially when they were so few in the first place, why not live among humans for a while while kryptoforming the moon?

Well, Zod and crew had to go to Earth to find Clark and get the Codex out of him. It could have been simple laziness that made their decision to kyrptoform Earth. It's also possible that it's easier to kryptoform a planet that was similar to Krypton than to kryptoform a planet that is incapable of supporting human or Kryptonian life. Or, more than likely, there would have been no conflict if the Kryptonians made their new home on another planet in the solar system.

"You will give the people an ideal to strive towards. They will race behind you. They will stumble. They will fall. But in time, they will join you in the sun. In time, you will help them accomplish wonders."
--Jor-El

It's a recession when your neighbor loses his job: it's a depression when you lose yours.
-- Harry S. Truman